In 2012 the European Union was awarded the Nobel Peace Prize. What was once the European Coal & Steel Community, the committee wrote, had evolved into a "successful struggle for peace, reconciliation and for democracy and human rights." Theres much to be said for the thought that Europes economic integration has led to lasting peace. But the crisis in Ukraine shows that global interdependence can be a source of weakness as well as strength.

After the Crimean invasion a British official was photographed holding a document recommending that the U.K. oppose "trade sanctions" against Russia or any measure that would "close Londons financial centre to Russians." Germany gets 35% of its gas supply from Russia. Europe, by and large, has been even more reluctant than America to challenge Vladimir Putins land grab.

For a time it was the U.S. Republican Party that most vociferously opposed military adventures. Robert Taft, the Senate majority leader known as "Mr. Republican," inveighed often against FDRs involvement in World War II. War, said Taft, would result in "the practical establishment of a dictatorship in this country through arbitrary powers granted to the President, and financial and economic collapse…Nor do I think that our intervention in Europe can permanently solve the European problems any more than it did in 1919."

Taft was certainly right about that last part. The European problem has not been permanently solved.

The challenge is that people dont sort themselves neatly into the ethnocentric nation-states that Woodrow Wilson longed for. From Quebec to Scotland to Catalonia to Crimea to Kashmir, one mans country is another mans landlord. Putin has reportedly called the breakup of the Soviet Union the "greatest geopolitical catastrophe" of the 20th century, not least because it left 25 million ethnic Russians outside of Russian borders.

We Americans have tried valiantly to see these as issues for others to address. But if Russia continues to annex Russophone enclaves in eastern Europe, these problems will avoid us no longer. Will Putin test the borders of NATO? What happens when China annexes the South China Sea or, worse, Taiwan?

Over the mid to long term the U.S. can do much to blunt Russias leverage over Europe, principally by exporting oil and gas to the continent. But China, with its $1.3 trillion in U.S. Treasurys and $562 billion in annual bilateral trade, is trickier.

Despite Republicans criticism of President Obama, there are no easy alternatives. In an incoherent op-ed for Time Republican Senator Rand Paul counseled suspending U.S. aid to Ukraine and getting Europe to pay for costly American missile-defense systems, while also saluting Ronald Reagans program of "peace through strength," a success that Reagan achieved thanks to a deficit-financed military buildup that Paul would today oppose.

President Obama famously declared in 2009 there would be a "reset" in U.S.-Russian relations, one whose central plank was the forgiveness of Russias 2008 invasion of Georgia. In 2001 Putin told George W. Bush a moving story about a cross Putins mother had gotten blessed in Jerusalem; Bush subsequently said that he had obtained "a sense of [Putin's] soul." Failure to address Russias growing belligerence has been bipartisan and multinational.

This is how wars begin. Democratic economies fear the material downside of confronting aggression, even if it would prevent a wider conflict. We often talk about learning the "lessons of history." But G.W.F. Hegel once observed that "what experience and history teach is this–that people and governments have never learned anything from history."

The "end of history" is not yet upon us. Free trade and the expansion of democracy have done much to reduce conflict around the world. But so has American hegemony. The U.S. will find relinquishing its leadership is far more expensive than maintaining it.